1. Field of the Invention
The present invention relates generally to improvements in synthetic thermoplastic compositions, articles made from such synthetic thermoplastic compositions and methods of making articles.
2. Description of Related Art
Plastics are moldable chemically-fabricated (synthetic) materials derived mostly from fossil fuels, such as oil, coal or natural gas. The long molecules in plastics are composed of carbon atoms linked into chains. One type of plastic, polyethylene, is composed of extremely long molecules, each containing over 200,000 carbon atoms. These long molecule chains give plastics unique properties and distinguish plastics from materials such as metals that have crystalline structures. Fossil fuels contain hydrocarbons, which provide the building blocks for long polymer molecules. The building blocks called monomers link together to form long carbon chains called polymers. The process of forming these long molecules from hydrocarbons is called polymerization. The molecules typically form viscous sticky substances known as resins which are the materials used to make plastic products or articles by heating the resins to their specific melting range and molding them into articles by various methods.
The carbon backbone of polymer molecules often bond with smaller side chains consisting of other elements, including chlorine, fluorine, nitrogen and silicon, for example. These side chains give plastics distinguishing characteristics. For example, when chlorine atoms substitute for hydrogen atoms along the carbon chain, the result is polyvinyl chloride, one of the most versatile and widely used plastics in the world. The addition of chlorine makes this plastic harder and more resistant. The advantages and disadvantages of different plastics are associated with the unique chemistry of each plastic which determines the physical, mechanical and thermal properties of the molded article.
All plastics can be basically divided into two groups: thermoplastic and thermosetting plastic. The two groups differ in the way that each responds to heat. Thermoplastics can be repeatedly softened by heating, and hardened by cooling. Thermosetting plastics harden permanently after being heated once. The present invention is concerned with the thermoplastic family of plastics.
Examples of commonly used thermoplastics are: polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS), polymethyl methacrylate (PMMA), polyamide (PA) and polycarbonate (PC). In addition, many variations and hybrid engineered resins based on these are in use today.
The process of forming plastic resins into products is the basis of the plastics industry. Many different processes can be used to make products from thermoplastics. Some of the more common of these processes are injection molding, extrusion molding, blow molding, injection blow molding, blow film extrusion, calendaring, thermoforming, casting and expansion processes. In all these processes, the plastic must be softened or sufficiently liquefied in order to allow the resin to flow and create the shape of the article. For convenience, all these plastic resin forming processes will be simply referred to as “molding process” hereinafter.
Because of the importance of thermoplastics to the production of consumer products, and the great number of consumer products made from thermoplastics, the industry is continually searching for ways to improve both the plastic resin systems, and the manner in which an article is made. Specifically, the plastics industry wants to create articles that have specified chemical and physical strengths, that have better color dispersion, and have improved surface smoothness and texture. The industry is also constantly searching for molding process improvements that reduce:                (a) cycle time, the amount of time needed to produce each article;        (b) cure time, the amount of time needed after molding for the article to be sufficiently hard to be handled;        (c) energy consumption per article, and        (d) operating temperature, for both energy conservation and prevention of polymer degradation.        